There has been a conventional DC power-supply device, in which a rectifying circuit, connecting rectifying diodes in a full-bridge configuration, rectifies single-phase or three-phase AC commercial power, or the like, and a series-connected switching element group performs switching of the output of the rectifying circuit to store energy in a reactor provided at the previous stage or the subsequent stage of the rectifying circuit, and to charge a capacitor with this energy, which is connected in parallel to the switching element group, thereby supplying a boosted DC voltage to a load. In the DC power-supply device as described above, it is general to change the boost ratio by means of changing the switching, and changing the energy to be stored in the reactor. However, there is a problem that when the switching frequency is increased, a switching loss is increased.
To the problem as described above, a technique to change the boost ratio without changing the switching frequency has been disclosed in Patent Literature 1 listed below, for example. In this technique, in the case of decreasing the boost ratio, a first switching element and a second switching element are turned on/off simultaneously. Also, in the case of increasing the boost ratio, a state transition is repeated, in which the first switching element and the second switching element are turned on simultaneously, one of the switching elements is only turned on, the first and second switching elements are turned on simultaneously, and the other switching element is only turned on.
Patent Literatures 2 and 3 listed below disclose a technique to control an input current into a sine waveform. These Patent Literatures are mentioned later in the descriptions of the embodiments of the present invention.